Aprit 4, 1884.] 
width of seven to ten miles. Through this 
it slowly ate its way, making a clear, clean 
path, and finally appeared on the lower side 
within five miles of Hilo. When within less 
than two miles of the village, it divided into 
two branches, one still continuing directly 
toward the village, and the other taking a 
course toward the Waiakea sugar-mill, which 
is about one mile south of Hilo. Finally, in 
the middle of August, 1881, the flow suddenly 
ceased, when the 
Hilo branch was just one 
mile from the town-house, and the Wailakea 
branch thirty-six hundred feet from the mill. 
It had then been flowing a little more than 
nine months, and had passed over a distance 
of about forty-five miles. 
I arrived in Hilo on the 8th of September, 
1881, and immediately visited the flow. ‘This 
was about three weeks after its cessation, but I 
found it still very warm. Standing on Halai, 
a small crater-cone near its lower extremity, 
nearly its whole length could be traced by the 
steam arising from it after a shower. I found 
its surface to be seamed with cracks and fis- 
SCIENCE 
411 
sures in all directions. Some of these were 
mere cracks, while others were six and eight 
inches, perhaps more, in width. ‘This made 
walking over it rather difficult. There are two 
common forms of lava known there, — the pa- 
hoehoe (satin) and the a-a. The former, which 
is far the more abundant, has much the appear- 
ance of folded satin, and usually spreads out 
in broad, level fields. Sometimes it swells up 
through some hole in the surface, and forms 
large dome-like masses. The above view gives 
avery fair idea of this variety of lava. Thea-a, 
which forms only a very small portion of this 
flow, is very rough and jagged, and is almost 
impassable, being totally so to horses. An 
adequate description of this peculiar formation 
is impossible. It must be seen to be appre 
ciated. I have as yet seen no adequate ex- 
planation why lava sometimes takes this form. 
Analyses show the chemical constitution of the 
two varieties to be about the same. It seems 
to occur, without any particular reason, at 
yarious points on the flow, in areas varying 
from a few rods to an acre or so. In its pas- 
